According to the results of the nation-wide survey of nutrition made by the Ministry of Public Welfare, Japan in 1991, a Japanese calcium intake is 540 mg/day in average, which is considerably lower than the recommended calcium allowance specified by the same ministry, i.e., 600 mg/day. Shortage of calcium intake recently turned out to cause serious diseases, such as osteoporosis, hypertension, and large bowel cancer. In particular, osteoporosis easily causes fractures, and it is very likely that an aged patient suffering from a fracture of femoral neck or a compression fracture of the lumber vertebra gets bed-ridden. In fact, the second cause of making the aged become the bed-ridden is a fracture. It is said that the number of patients with osteoporosis has reached about 5,000,000 and will be increasing steadily to pose a serious social problem in an aging society ahead.
What is wanted to ameliorate the present situation is to increase a calcium intake so as to always supply sufficient amount of calcium to the body. However, an average Japanese' calcium intake per day has never exceed the recommended allowance (600 mg) according to the survey taken by the Ministry of Public Welfare every year, revealing difficulty to assure a sufficient level of a calcium intake through daily food. While calcium-containing pharmaceuticals and calcium-enriched foods are available, they are inferior in palatability and difficult to take habitually.
Under these circumstances, it is important, the inventors thought, that orally taken calcium be absorbed efficiently through the intestine, the absorption site for calcium. It is considered that the ratio of calcium absorbed through the intestine and utilized for maintenance of a living body in the total calcium orally taken is about 20 to 50%, while somewhat varying depending on the origin of calcium, so that the most of orally taken calcium is excreted without being absorbed. Therefore, an increase in percent absorption of calcium in the intestinal tract would fulfill the calcium requirement without forcing unnatural calcium intake.
Vitamin D and lactose are commonly used as a component which accelerates calcium absorption in the field of foods and pharmaceuticals. Because vitamin D is biosynthesized, administration of vitamin D is not expected to act for acceleration of calcium absorption in those who can synthesize sufficient vitamin D in their own body. Lactose is not favorable to those who suffer from lactose intolerance because of side effects, such as diarrhea.
Additionally, peptide of bone origin (see JP-A-4-16165, the term "JP-A" as used herein means an "unexamined published Japanese patent application") and a composition mainly comprising butyric acid (see JP-A-4-108360) have been proposed as a component for calcium absorption acceleration. However, neither of them has been put to practical use due to involvement of problems in production and use.
It is known that oral intake of calcium in combination with other food components results in a slightly increased calcium absorption as compared with single calcium intake. This phenomenon is accounted for as follows. Food entering the stomach stimulates secretion of gastric juice to lower the gastric pH value so that calcium, which is generally water insoluble, is dissolved by the action of the acid and thereby becomes ready to be absorbed. However, in what manner a food component takes part in absorption of calcium through the intestine has not been studied intensively.